A device of the general type to which the present invention is directed is described in U.S. Pat. No. 4,308,756, the disclosure of which is incorporated herein by reference. In that prior art, a sample carrier bearing a sample for analysis first is loaded onto a carrying fork or probe through a port in an intermediate vacuum chamber while the loading device is isolated from the ultra high vacuum analysis chamber. Following closure of the sample introduction port, the intermediate chamber is pumped down to the ultra high vacuum range (less than 10.sup.-6 mm of mercury). An air lock valve located between the loading chamber and the main ultra high vacuum analysis chamber then is opened to establish communication between the chambers and the sample carrier. The loading fork is moved into the analysis chamber by extending an elongate probe arm to which the loading fork is mounted and may be manipulated to a position to deposit the sample carrier at any desired location in the analysis chamber. After so positioning the sample carrier, the probe arm and loading fork may be retracted from the analysis chamber and the air lock closed again.